The prevention of disability has been the driving force behind much research. In epidemiology three levels of prevention are defined: primary, secondary, and tertiary prevention. Primary prevention is the prevention of the initiation or occurrence of a disease; secondary prevention is the prevention or amelioration of the consequences of a disease, and tertiary prevention refers to rehabilitation or the limitation of disability associated with the disease. We have examples of all three levels of prevention in the area of childhood disability. Primary prevention is the protection of infants against congenital rubella syndrome by ensuring that women of childbearing age have adequate immunity before they become pregnant. The prevention of choreoathetosis, mental retardation, and deafness, by treating hyperbilirubinemia and preventing kernicterus in newborns, is a great success story in prevention. Similarly, at the level of secondary prevention, is the reduction in mental retardation caused by phenylketonuria, or PKU, by eliminating phenylalanine in the diets of newborns who lack the enzyme to metabolize this amino acid. Tertiary prevention is the area of rehabilitation medicine, and is regarded as the least desirable level of prevention. Indeed, tertiary prevention can be seen as “doing the best we can” in terms of rehabilitation, often while seeking a means of really preventing the disease.